The present invention relates to a nickel crucible for melting an analytical sample, a preparation method of such analytical sample, and a method of analysis that enables high precision analysis by inhibiting the mixture of impurities from the crucible regardless of who or how skilled the analyst is.
In recent years, demands for measuring high purity materials quickly and accurately are on the rise. Particularly, since persistent samples are increasing in recent years, a flux with stronger oxidizing power is in demand.
A persistent sample is generally prepared by melting the sample with a flux. The process of melting the sample with a flux is usually based on a melting method such as carbonate (alkali) fusion, alkali hydroxide fusion, sodium peroxide fusion, or sodium hydrogensulfate fusion. Nevertheless, if a flux with strong oxidizing power is used, the crucible itself will wear easily, and, consequently, there is a problem in that impurities will be eluted in the crucible.
In other words, according to the increase of the foregoing demands, there is a problem in that the measured values differs due to the influence of contamination from the used equipment, and often reanalysis must be performed in order to confirm the reliability of the initial analysis.
As described above, since a conventional nickel crucible for melting a sample has a purity level of 99wt % (2N), there is a problem in that the lower limit of determination will increase due to the mixture of impurities from the crucible, and such conventional nickel crucible cannot be used for analyzing the recent high purity samples. Nevertheless, conventionally, no attention was particularly given to the purity of crucibles, and the situation ends with that the measurements were merely conducted several times or the pretreatment process was devised in certain ways.
Although there are not many Patent Documents that describe an analytical means to handle the foregoing high purity materials, take some materials that may be of reference, for instance, there is technology that relates to the method of adjusting a sample for performing qualitative and quantitative analysis of such sample, whereby the sample is placed on a metal foil and subject to thermolysis together with such metal foil, and further made into a solution (Patent Document 1). Nevertheless, this is an extremely atypical type of method, and lacks versatility.
Further, a chemical analysis crucible composed from Pt alloy or Pd alloy in which 5 to 90wt % of Pd is added to Pt that uses an alkali flux to perform chemical analysis of ores is disclosed (Patent Document 2). Nevertheless, this technology is subject to the use of expensive crucible materials, and there is a problem in that it is impractical since an alloy will be formed depending on the sample elements.
In addition, a method of analyzing the rhodium content in a film by heating and melting a rhodium-ruthenium alloy plating film in a nickel crucible with sodium peroxide or potassium peroxide is disclosed (Patent Document 3). Nevertheless, Patent Document 3 does not in any way disclose the purity of the crucible. Thus, it is strongly assumed that the crucible of Patent Document 3 has a conventional purity level (2N level). Thus, there is a problem in that the lower limit of determination is high due to the inclusion of impurities, and high precision analysis cannot be performed.    [Non-Patent Document 1] “Analysis” Introductory Course, Issued in October 1979, “Reagent Used in Dissolution” Pages 648 to 655    [Patent Document 1] Japanese Patent Laid-Open Publication No. H10-38773    [Patent Document 2] Japanese Patent Laid-Open Publication No. H2-172540    [Patent Document 3] Japanese Patent Laid-Open Publication No. S58-48854